The overall aim is study of the role of growth factors in colonocyte differentiation using the cell bank developed by this laboratory from one parental line. These include colon carcinoma cell lines permanently committed to enterocytic, fluid-transporting differentiation, HD3, HD4, and U4H, one enterocytic precursor cell line U4, and one line blocked in enterocytic maturation, HI1. All of these cell lines exhibit autocrine negative growth regulation by TGFbl. A second group of cell lines include those committed to goblet cell differentiation, HD6 and HD8, which display no modulation by TGFbl. The third group contains multilayered cell lines resistant to differentiation by HMBA, U9 and HP1, which utilize TGFbl as an autocrine positive growth regulator. It will be determined whether cells committed to enterocytic differentia- tion, HD3, HD4 and U4H, respond by growth inhibition to TGFbl through hypophosphorylation of the retinoblastoma gene product and where this occurs during the cell cycle and whether TGFbl-resistant cell lines maturing to goblet cells, HD6 and HD8, have lost TGFbl receptors. Whether differentiation interrupts a TGFalpha autocrine growth stimula- tory loop will be studied by comparing expression of both the ligand and receptor in differentiated and undifferentiated cells. The mechanism for loss of mitogenic response to basic FGF by differentiated colon carcinoma cells and whether autocrine FGF pathways exist in undifferentiated lines will be determined. Three possible indirect mechanisms for TGFbl-stimulation of growth of undifferentiated colon carcinoma lines will be examined. The effect of a transfected activated v-H-ras gene on goblet cell and enterocytic differentiation will be examined as will be the necessity of cell to cell contact through the L-CAM uvomorulin for enterocytic and goblet cell differentiation.